There's a never-ending stream of scientific explanations for obesity. The latest suggests that carbon dioxide contributes to our weight gain, and that as we pump more of it in to the atmosphere, the fatter we become. But can that really be the case?
The theory is favoured by Lars-Georg Hersoug, a scientist from Denmark. He suggests that orexins -- hormones in the brain that influence energy expenditure and food intake -- are affected by CO2. Affected so much, in fact, that they can shift our metabolism and make us fat.
He has some evidence. Firstly, the rise in obesity in the US was fastest in the period 1986-2010 on the East Coast, where CO2 concentrations are highest. Second, that in animal tests, environmental factors -- he can't say exactly which -- contribute to weight gain. And third, that inhaling CO2 makes our blood more acidic, something that has been linked to changes in orexins.
Some of this sounds reasonably convincing, some of it less so. But the theory doesn't hold much sway amongst his peers. Speaking to Science Nordic, Thorkild I. A. Sørensen, the leader of the Danish Obesity Research Centre, said:
"[He's] quite right in showing interest for other possibilities. [The] hypothesis is a new and very interesting idea, clearly inspired by studies using animals in captivity that have also put on weight — and a common factor for these animals and people is the air we breathe.
"But there is one problem: the obesity epidemic has developed quite irregularly in time and place, even in a small country such as Denmark, and only a part of the population is affected even though we all breathe the same air."
While it would be wonderful to point to a scientific explanation for the obesity epidemic -- especially one that is out of our immediate control -- the fact remains that we're getting fat and need to do something about it. CO2 might cause some very small increase in weight in some of the population, but it's not what we need to worry about. We need to worry about losing weight instead. The most effective way to do that? Eat less and exercise more. [Science Nordic]